NTC thermistor is a negative temperature coefficient resistor (power thermistor), whose resistance value decreases with increasing temperature. It is widely used in switching power supplies, module power supplies, temperature sensors, UPS power supplies, electronic ballasts, automatic regulation heating and other places.
NTC thermistor is small in size and high in power. It is mainly used in power supply circuits to suppress surge current and is generally connected in series to the mains input. It has a rated zero-power resistance value. When connected in series in the power supply circuit, it can effectively suppress the startup surge current, and the power consumption is almost negligible.
Usually when the switching power supply is turned on, there will be a high peak surge current to charge the filter capacitor and thus charge the device. These surge currents will affect the service life of the capacitor and damage the contacts of the power switch or destroy the rectifier diode. Therefore, it is necessary to take corresponding solutions.
Using NTC thermistor to suppress the inrush current of switching power supply is a low-cost and simple method, as shown in the figure below:
AC to DC power supply module refers to a small switching power supply composed of AC-DC rectifier circuit, DC-DC converter and a small number of components. Connecting an NTC thermistor can effectively suppress the surge current applied to the input and output capacitors when power is turned on. As shown in the figure below:
In DC power supply circuits such as DC-DC converters, NTC thermistors are used as power thermistors, which can effectively suppress inrush currents, and input and output capacitors are charged when the power is turned on. The resistance of the NTC thermistor becomes very low after power is turned on, achieving lower power loss than when using fixed resistors. As shown in the figure below:
![]()
The following is a brief introduction on how to select NTC thermistors. There are many parameters of NTC thermistors on the Internet, among which the 25-degree ohm value and B value are important parameters. The 25-degree ohm value determines the current limiting capability of the NTC at the moment when the power circuit is powered on, and the B value can calculate the resistance value of the NTC when it reaches the final temperature. The equation is as shown above: R1 and R2 are the resistance values at absolute temperatures T1 and T2 respectively. As shown in the figure above: B0/50, B25/50, B25/75, B25/85 and B25/100 correspond to the B values between different temperatures respectively. Assuming that the resistance is 10 when the temperature is 25 degrees, and the resistance is 2 when the temperature is 85 degrees, the B value needs to be above 2864K.
For some applications where reducing power consumption is critical, the power loss of NTC thermistors cannot be ignored. According to actual conditions, a relay can be connected in parallel to the NTC thermistor to reduce the power consumption of the NTC thermistor. Ordinary resistors can be used instead of NTC thermistors to act as current limiting resistors.
提升卡
变色卡
千斤顶
京公网安备 11010802033920号
